Chris, would you know if the 3-Mile section was ever signed? Or actually was designated as a state road, as opposed to being planned? That would simplify things.

Well, funny you ask... As I've been researching M-114—which isn't something I've done thoroughly until now—I'm starting to answer my own question, although I need to do more research. First, the West-, South-, and East Beltlines were all signed as M-114, although the portion of East Beltline from US-16/Cascade Rd southerly to Laraway Rd (28th St) may have been only signed as BYP US-131 (and BYP M-21?) upon its completion in 1942–43. In any event, it was sometime during WWII that the west, south and east sides of the "box" were given the bypass designations and the M-114 was removed. It seems like 3 Mile Rd was never signed as M-114 prior to c.1942–43, but may have been signed from East Beltline westerly to Monroe Ave just as the signs came down on the rest of it (c.1942–43). Since the official highway maps of the time never showed M-114 along 3 Mile Rd—likely because the long-proposed Grand River bridge was never constructed—I'm still not sure if any part of 3 Mile was signed as M-114 in the field. I have several old MDSH sources which show the route as M-114, but that doesn't necessarily mean it was actually signed as such.

My M-114 research so far has been more concentrated on its determination in 1928 and when each segment was completed and opened to traffic. Next I'll try to see if I can dig up any information as to what happened during the War and if the 3 Mile segment(s) were ever signed, but Wartime highway information tends to be a little harder to find and if it wasn't signed, it'll be even more difficult to find info on.

Oh, no, I'm aware of those routes, although, truth be told, I just recently discovered the proposed-but-never-built M-144 northwest from Lake Odessa. (I'd known about the proposal, but hadn't seen the M-144 designation applied to it until recently.) I will be incorporating these early incarnations of M-117 and M-144 into their respective route listings as I migrate them to the new format in the near future. I've found a few route designations on the old biennial report maps that never seem to have made it to reality (for those roads that were eventually constructed, unlike the proposed M-144) that were never likely signed in the field with the designations indicated on the map, such as M-123 on M-126 between Nunica and Muskegon. So, at this point, the M-117 designation at Frankenmuth may never have made it past the planning documents, but I'll definitely be researching it anyway!

Usually in a loop situation, "Mile 0" is along the southern or western leg...thinking specifically of the I-494/694 loop in the Twin Cities (Mile 0 at the Minnesota River) or pre-95-cancellation I-495 around DC (Mile 0 was at the Woodrow Wilson Bridge).

In this case, you have the three spurs, which I would treat separately, and also what appears to be a gap between C and D. If that gap is legit, I'd go with D as "Mile 0" and increase going clockwise, again treating the spurs separately.

Yeah, I'd considered using either the modern-day beltway numbering system as suggested by the Feds or starting at the gap where the bridge was never constructed over the Grand River north of downtown, but as I've been doing my research, it looks like the final incarnation of M-114 (whether or not it was signed as such is unclear) was just along the northern segment: A–C and D–E and my practice with the former route listings is to use their last set of termini prior to being decommissioned/cancelled/nuked. During M-114's lifetime, though, it seems like only the west and south sides ("A" to "H") and the portion of the east side from "F" south to US-16/Cascade Rd was signed as M-114 and not the Cascade Rd–to–28th St portion which may have opened to traffic signed as BYP US-131/BYP M-21 during WWII, although some sources show that segment may have been at least graded and open to traffic willing to brave an unsurfaced, unimproved route but may not have been posted as part of any state highway route. So, my original question may now be moot, but I'm still researching...